Turn heavy PNGs into light JPGs. For photographic images that don't need transparency, the size drop is usually dramatic.
PNG is lossless, which makes it ideal for screenshots, diagrams, interface mock-ups and anything with crisp text. For photographs it is wasteful: a camera image stored as PNG can be far larger than the same image as a JPG, with no visible benefit. That is the usual reason to convert — a photo that ended up as a PNG after a screenshot, an export or a download, and is now too heavy to email, attach or upload.
JPG has no transparency at all. Every transparent or partly transparent pixel is composited onto white before encoding, so a logo on a transparent background comes out as a logo on a white rectangle, and soft shadows fade into white. This happens silently; there is no prompt first. If you need the see-through background but want a smaller file, use Compress instead — it keeps a PNG as a PNG, transparency included, and shrinks it by reducing the colour palette.
The buttons set quality 62 (Smaller), 82 (Recommended) and 94 (High); the slider goes from 40 to 100. For photos, Recommended is usually the right balance between size and appearance. For screenshots and graphics with hard edges, pick High or reconsider whether JPG is the right target. Each output file keeps the original name with _conv and a .jpg extension, and many files can be downloaded together as one ZIP.
Everything runs inside your browser. Because the image never reaches a server, we cannot store it or look at it. That difference matters when the file is company material or a personal photo.